Segmental time reversal device



Dec. 8, 1964 H. L- LIBBY ETAL 3,160,817

SEGMENTAL TIME REVERSAL DEVICE Filed July 9, 1962 2 Sheets-Sheet 2 QLJINVE TORS flgyo Z2. Ltfb] Y James ,Z'jzzssell Q, a g a. M

- flfiorflgy United States Patent 3,160,817 SEGMENTAL TIME REVERSALDEVICE Hugo L. Libby and James T. Russell, Richland, Wasln,

assignors to the United States of America as represented by the UnitedStates Atomic Energy Commission Filed July 9, 1962, Ser. No. 208,653 2Ciaims. (Cl. 328-56) This invention relates to an electrical circuit forsegmentally reversing in time an electrical signal.

In the manipulation of electrical signals containing information it isoften useful to reverse the signal in time and then operate on the timereversed signal. This is particularly true with signals havingexponential components which die away as time advances where it isnecessary to analyze and decompose the signal into orthogonalexponential components. Application for this type of operation is foundin the nondestructive testing art in the analysis of signals from theobject undergoing test. Present techniques use magnetic tape recordings.However, these methods present difficulties for segments of smallduration and become uneconomical when high frequency components exist.

It is therefore one object of the present invention to provide a devicefor reversing in time an electrical signal.

It is another object of the present invention to provide a device forreversing in time an electrical signal whereby the reversed signal hasan expanded or compressed time base with respect to the original signal.

It is still another object of the present invention to provide a devicefor segmentally reversing in time a periodic electrical signal.

It is yet another object of the present invention to provide a devicefor segmentally reversing in time a periodic electrical signal wherebyreversal or nonreversal of segments thereof may be accomplished asdesired.

I Other objects of the present invention will become more apparent asthe detailed description proceeds.

In general the present invention comprises a first electric transmissionline whose sections are connected via switching circuits to associatedsections on a like second electric transmission line. A periodic signalis applied to the first transmission line causing a travelling wave tobe established thereon. At predetermined time intervals, the switchingcircuits are energized and permit the travelling wave existing on thefirst transmission line to be switched to the second transmission linewhere it causes travelling waves to be propagated therealong in twoopposing directions. One of these propagated waves is time reversed withrespect to the original signal and hence, when detected at one end ofthe second transmission line, provides segmental time reversal of theinput signal.

Further understanding of the present invention will best be obtainedfrom consideration of the accompanying drawings in which:

FIG. 1 is an illustration of a device for the present invention.

FIG. 2 is an electrical schematic of a preferred embodiment of thedevice of FIG. 1.

FIG. 3 is graphical representation of the input and output signals ofthe embodiment of FIG. 2.

FIG. 4 is an electrical schematic of an alternate device for the presentinvention.

The device of FIG. 1 is shown to illustrate the basic device for thepresent invention and to facilitate the explanation of the operationtherefor. The device comprises a first electrical transmission linehaving distributed or lumped parameters and a second identicalelectrical transmission line 12. Switching circuits 14 interconnectassociated sections of each of the transmission lines 10 and 12.

3,160,817 Patented Dec. 8, 1964 In operation, the signal to be reversed16 is applied to the end of transmission line 10, causing a travellingwave 18 to be established thereon. For the purposes of illustration onecycle of periodic signal 16 is shown on the transmission line 10 withthe leading edge thereof approximately at the end of the line 10. Atthis time, 1:13, switching circuits 14 are actuated which causes thetravelling wave 18 on line 10 to be transferred to transmission line 12.This establishes a wave 20 on line 12 which propagates in two opposingdirections thereby forming two travelling waves 22 and 24. The wave 22travelling towards the far end of line 12 is similar to that on line 10and is dissipated in a line terminating resistor. The wave 24 travellingtowards the near end of line 12, is reversed with respect to that online 10, its leading edge. being formed by the trailing portion of wave18 and its trailing edge being formed by the leading portion of wave 18.The reversed wave 24 appears across a terminating resistor at the nearend of line 12 as a signal 26 having a waveform as shown. Thus, byswitching travelling wave 18 at time intervals of t, it may becontinuously segmentally reversed, the signal of a subsequent cyclebeing fed onto line 10 while the time reversed signal of the priorperiod is being read at the near end of line 12.

FIGURE Zillustrates a detailed embodiment for the device of FIG. 1. Afirst electric transmission line 28 is composed of six L-C sections 30.The inductance of each section30 is 60 millihenrys and the shuntcapacitance 0.002 microfarad. The time delay for each of the section 30is approximately 11 microseconds and the line 28 has a cutoff frequencyof 30 kc. with a characteristic impedance of approximately 5600 ohms.The second electric transmission line 32 is identical to the first line28. Switching circuits 34 interconnect associated sections 30 of thetransmission lines 28 and 32. Each of the switching circuits consists ofa 2200 ohm resistor 36 connected in series with a diode 38 across theassociated sections of the lines 28 and 32. A phanastron time delaycircuit and blocking oscillator (not shown) provide a switching impulseof about one microsecond which is fed via coupling capacitor 39 to thejunction of the resistor 36 and diode 38. A biasing circuit (not shown)provides a back bias voltage for each of the diodes 38, therebypermitting significant diode conduction only during the switchingimpulse.

Operation of the embodiment of FIG. 2 is similar to that previouslydescribed for the device of FIG. 1.

The waveform 40 shown in FIG. 3 was applied to the near end oftransmission line 28. Waveform 42 was detected across terminatingresistor 44 at the near end of transmission line 32. Thus, it can beseen that the output voltage from the embodiment of FIG. 2 is asegmental reversal of the input signal thereto. The time of switching isshown by the small pip 46 near the center of both waveforms 40 and 42.

With the above described embodiment several arrangements are possible bywhich the waveform of a signal may be controlled and adjusted over awide range. Expansion and compression of the time base of the reversedsignal may be accomplished by varying the design of the secondtransmission line 32. For example, the output signal time base may becompressed by reducing the time delay of the second line and keeping thenumber of switching points unchanged. Conversely, expansion may beaccomplished by increasing the time delay. Differential expansion incompression of the time base may be accomplished by shortening orlengthening diiferent sections of the second transmission line 32 whilemaintaining the number of switching points unchanged. Selected portionsof the input signal can be eliminated from the output signal by omissionof appropriate switching circuits and certain portions of the inputsignal may be Thus, a wide variety of control over the output waveform42 may be obtained by using various combinations of these techniques. 6

In FIG. 4 an alternate embodiment for the practice of the presentinvention is disclosed. A single electrictransmission line 48 having aplurality of L-C sections 50 is used as one arm of a bridge circuit 52.The other three arms of bridge circuit 52 are composed of resistors'54,.

56 and .58. "A'phantastron time delay circuit 57 and blocking oscillator59 provide a switching impulse through diodes 60 to each of the L-Csections 50 of transmission line 48. I

In operation, the input signal is applied across the transmission line48 and resistor arm 54 of bridge 52. The bridge is balanced; therefore,no output signal appears across the output terminals 62 and 64 of thebridge 52. The applied signal travels down transmission line 48'asin thepreviously described embodiment of FIG. 2. At the appropriate moment,when the portion of the applied signal to be reversed is all on thetransmission line 48, the switching impulse is applied to the diodes 60.The switching impulse causes all the capacitors in the L-C sections 50to be charged to a potential approximately equal to the peak value ofthe input pulse. A change in the charge of the capacitors of the L-Csections will occur at this time, dependent upon the difierence betweenthe peak value of the swiching impulse and the, then existing potentialon the capacitors due to the initial wave travelling down thetransmission line 4%. Depending upon this ditference a reverse wave willbe generated travelling toward the near ,or input end of transmissionline 48. This signal will appear at the output terminals 62 and 64 ofbridge 52 and will be segmentally time reversed but will be inverted andwill be accompanied by. a pedesa 4' should not be limited totheparticular embodiments thereof shown in the drawings and described abovebut shall be determined only in accordance with the appended claims.

What is claimed is: V

1. A device for segmentally reversing in time a periodic signalcomprising an electric transmission line having a plurality ofcapacitor-inductor sections, a balanced electrical bridge having fourimpedance arms, said transmission line forming one of the impedance armsof said bridge, the input to said bridge being across said transmissionline and an adjacent arm of said bridge, the output of said bridge beingacross said transmission line and the other adjacent arm of said bridge,means for apply ing said periodic signal to the input of said bridge togenerate a periodic traveling wave on said transmission'line,

and means responsive to said periodic traveling wave for charging thecapacitors of said sections of said transmission line whereby atraveling wave is propagated on said transmission line. in reverse tosaid periodic traveling wave, said reverse traveling wave appearing atthe output of saidbridge and being in time reversal with respect to saidapplied signal.

2. The device according to claim 1 wherein said periodic signalresponsive means comprise a phantastron time delay circuit, a blockingoscillator and a plurality of diodes, said phantastron circuit andblocking oscillator providing a voltage impulse through said diodes toeach of the capacitor-inductor sections of said transmission line whensaid periodic signal is present on said transmission line, whereby thecapacitors thereof are caused to charge to a voltage approximately equalto the peak value of said applied voltage impulse.

References Cited by the Examiner UNITED STATES PATENTS 4/ 41 Australia.

JOHN w. HUCKERL Prirnary Examiner. GEORGE N. WESTBY, Examiner.

1. A DEVICE FOR SEGMENTALLY REVERSING IN TIME A PERIODIC SIGNALCOMPRISING AN ELECTRIC TRANSMISSION LINE HAVING A PLURALITY OFCAPACITOR-INDUCTOR SECTIONS, A BALANCED ELECTRICAL BRIDGE HAVING FOURIMPEDANCE ARMS, SAID TRANSMISSION LINE FORMING ONE OF THE IMPEDANCE ARMSOF SAID BRIDGE, THE INPUT TO SAID BRIDGE BEING ACROSS SAID TRANSMISSIONLINE AND AN ADJACENT ARM OF SAID BRIDGE, THE OUTPUT OF SAID BRIDGE BEINGACROSS SAID TRANSMISSION LINE AND THE OTHER ADJACENT ARM OF SAID BRIDGE,MEANS FOR APPLYING SAID PERIODIC SIGNAL TO THE INPUT OF SAID BRIDGE TOGENERATE A PERIODIC TRAVELING WAVE ON SAID TRANSMISSION LINE, AND MEANSRESPONSIVE TO SAID PERIODIC TRAVELING WAVE FOR CHARGING THE CAPACITORSOF SAID SECTIONS OF SAID TRANSMISSION LINE WHEREBY A TRAVELING WAVE ISPROPAGATED ON SAID TRANSMISSION LINE IN REVERSE TO SAID PERIODICTRAVELING WAVE, SAID REVERSE TRAVELING WAVE APPEARING AT THE OUTPUT OFSAID BRIDGE AND BEING IN TIME REVERSAL WITH RESPECT TO SAID APPLIEDSIGNAL.